Win HOW TO - Launch MPC-HC/MPC-BE with madVR as an External Player
Your NAS is most likely streaming ok since you can open the file via Explorer but try copying the file local and see if it opens correctly.
Right click the mkv file and select open with MPC-BE instead of using MPC-BE 'open file'.
If this works, imo KODI v.18 is at fault.

"failed to render file" usually means the external player simply fails to read it.  In my case, I see this when trying to play full rip iso's before automating a mount via scripts.  I have seen one other post that MPC players do not need to mount an iso before they can play it but I don't see how this could be possible.  This is why I ask to check the NAS stream because failed to render sounds like MPC just doesn't see the file.  This could be a miscommunication from KODI and the playercorefactory though?

 I have been trying v.18 for some time now including todays latest nightly.  While I can open a file with an external player launched from KODI, no amount of selecting WHICH external player obeys the playercorefactory or the KODI 'open with' menu performs.  Reverting to v.17.6 all is well.  You might give the revert a try as it should perform as expected until a Windows developer joins the KODI team and desires to tackle playercorefactory.xml and external player hurdles.
HOW TO - Kodi 2D - 3D - UHD (4k) HDR Guide Internal & External Players
W10/2004 MPC-BE\HC PDVD19 DVDFab3&5 KODI 19 PotPlayer 960-4GB/RGB 4:4:4/Desktop=60Hz/Video=Matched Refresh rates 8/12bit/Samsung 82" Q90R

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RE: HOW TO - Launch MPC-HC/MPC-BE with madVR as an External Player - by brazen1 - 2018-04-29, 21:29

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